There are four basic categories of calcium-silicate cements distinguishable by composition and production methods. These four materials -- Portland cement, hydraulic lime, and pozzolanic cement -- are discussed in terms of component oxides and their behavior in relation to setting time, heat of hydration reaction, onset of strength, and corrosion resistance. References to cement in ancient literature are evaluated in terms of the properties of the materials; literary evidence suggests a restricted, not clearly defined use of hydraulic limestones and indicates a knowledgeable, purposeful use of pozzolans. Analysis of ancient cements does not provide conclusive evidence for the existence of a particular cement technology; hydration and other changes in the component oxides, carbonates, and hydroxides obscure the original technological process. -- AATA